To each LED a brightness value between 0 (off) and 255 (freakin' bright) can be assigned.
If one preferrs percentage values, as a convenience function all values smaller than 1 are treated as percentage values. Note that the value of '1' is not treated as 100% but as the brightness value of 1!

This module also exposes its internal structure, with the possibility to invoke the piGlow interface with a injected mocking backend.
There are two backends, BackendMock prints the piglow data as JSON, BackendMockPrettyPrint structures the data in a readable way.

var piGlow =require('piglow');

var PiGlowBackendMock = piGlow.BackendMock;

var piGlowInterface = piGLow.piGlowInterface;

var myMock =newPiGlowBackendMock();

var myInterface = piGlowInterface(myMock);

//lets hack

myInterface.ring_0 =255;

This way the module can be used in a non raspi environment for development or with a testing mock for unit tests.
To implement your own mocks follow this interface: